1. Field of the Invention
The present invention generally relates to a valve timing control apparatus for controlling or regulating a valve open/close timing (hereinafter referred to simply as the valve timing) at which an intake valve and/or an exhaust valve of an internal combustion engine is opened and/or closed in dependence on operation state of the engine.
2. Description of Related Art
For having better understanding of the concept underlying the present invention, related techniques known heretofore will first be described in some detail by reference to FIGS. 22 to 26 of the accompanying drawings which shows a conventional valve control apparatus for an internal combustion engine (hereinafter also referred to simply as the engine).
In the figures mentioned above, FIG. 22 is a diametrical sectional view showing an internal structure of a vane-type valve timing regulating apparatus (which may also be referred to as the cam phase actuator), FIG. 23 is a vertical sectional view of the same taken along a line Axe2x80x94A in FIG. 1 and shows a structure in an axial direction, FIG. 24 is a partial perspective view showing a lock/unlock mechanism (lock pin retaining/releasing mechanism) and peripheral structure thereof in the cam phase actuator, and FIGS. 25 and 26 are vertical sectional views showing in detail a structure of the lock/unlock mechanism including a lock pin which constitutes a major part thereof and a peripheral structure provided in association therewith in different operation states, respectively.
Referring to FIGS. 22 to 26, the valve timing regulating actuator includes a first rotor assembly 1 (also referred to as the first rotor) which is constituted by a sprocket 2, a case 3 having a plurality of shoes 3a, a cover 4, and clamping members 5 for securing together the sprocket 2, the case 3 and the cover 4, in an integral structure. The first rotor assembly 1 mentioned above constitutes a part of an external rotatable member such as a crank shaft of the engine. (See FIGS. 22 and 23).
Disposed rotatably within the case 3 is a rotor (second rotor) 6 which constitutes an integral part of an internal rotatable shaft of the actuator and which includes a plurality of vanes 6a each of which is adapted to slideably move on and along the inner peripheral wall of the case 3. (See FIG. 23)
The cam shaft 7 includes a clamping member 8 which extends along the rotational center axis of the cam phase actuator. The spaces defined between radially projecting shoes 3a of the case 3 and the vanes 6a of the second rotor 6 cooperate to form valve timing advancing hydraulic chambers 9 and valve timing retarding hydraulic chambers 10, respectively. (See FIG. 23).
Communicated to each of the valve timing advancing hydraulic chambers 9 and valve timing retarding hydraulic chambers 10 are a first oil passage (hydraulic chamber feed passage) 11 and a second oil passage 12, respectively (FIGS. 22 and 23).
A fluid-tight seal means 13 is provided at a tip end portion of the projecting shoe 3a of each vanes 6a. 
A pin receiving hole 14 having a back pressure chamber 14a defined therein is formed in one of the vanes 6a, and a lock pin (lock member) 15 is accommodated within the receiving hole 14. The lock pin 15 is resiliently urged in a projecting direction (lock direction) under the influence of an urging means 16 such as a spring. (See FIG. 23).
A discharging hole 17 is formed in the back pressure chamber 14a of the receiving hole 14.
Communicated to the unlock hydraulic chamber 18a are a first unlocking hydraulic pressure feed passage 20 and a second unlocking hydraulic pressure feed passage 21 by way of a check valve 19. Exchangeably provided on the upstream side of the check valve 19 are a valve timing advancing hydraulic pressure distribution passage 22 and a valve timing retarding hydraulic pressure distribution passage 23, respectively. (See FIGS. 25, 26).
Further formed in a side wall of the receiving hole 14 is a purge passage 24 (FIGS. 25, 26) which serves to discharge through the discharging hole 17 the air trapped during stoppage of the engine, when the hydraulic pressure is fed from an oil pump (not shown) upon starting of engine operation.
By virtue of the arrangement that the air is forcibly discharged upon starting of the engine operation, a residual hydraulic pressure is generated by the oil supplied to the back pressure chamber 14a, whereby the unlocking of the lock pin 15 can positively be prevented (FIG. 25).
On the other hand, when the advancing hydraulic pressure is put into effect, the urging effort of the urging means 16 is overcome by the hydraulic pressure fed from the oil pump, as a result of which the tip end portion of the lock pin 15 is pushed in the unlocking direction, whereby the lock pin 15 is released from the locked state (FIG. 26).
FIG. 27 is a block diagram showing generally and schematically a structure of a conventional valve timing control apparatus for an internal combustion engine to which the present invention can find application.
Referring to FIG. 27, reference numeral 101 denotes generally an internal combustion engine which includes an air cleaner 102 for purifying the air sucked into the engine 101, an air-flow sensor 103 for measuring an intake air quantity (flow rate of the intake air) fed to the engine 101 and an intake pipe 104.
The intake pipe 104 is equipped with a throttle valve 105 for adjusting the intake air quantity (flowrate) to thereby control the output torque of the engine 101 and a fuel injector 106 for injecting an amount of fuel compatible with the intake air quantity.
Further, the internal combustion engine 101 is provided with an exhaust pipe 107 for discharging an exhaust gas resulting from combustion of the air-fuel mixture in the combustion chamber. Disposed within the exhaust pipe 107 are an O2-sensor 108 for detecting a residual amount of oxygen contained in the exhaust gas and a three way catalytic converter 109.
The three way catalytic converter 109 serves to purify concurrently harmful gas components contained in the exhaust gas such as HC (hydrocarbon), CO (carbon monoxide) and NOx (nitrogen oxides).
Further, the engine 1101 is provided with a spark plug 111 adapted to be driven by an ignition coil 110. The spark plug 111 serves to generate a spark for firing the air-fuel mixture charged in the combustion chamber of the engine with high-voltage energy supplied from the ignition coil 110.
A cam angle sensor 112 provided in association with the intake valve of the engine 101 generates a pulse signal upon every passing of a projection formed in a cam angle detecting sensor plate (not shown) for thereby detecting the cam angle.
At this juncture, it should be mentioned that although only the cam angle sensor 112 provided in association with the intake valve is shown, this is only for the convenience of description. It should be understood that the cam angle sensor can of course be provided in association with the exhaust valve or both of the intake valve and the exhaust valve.
Provided in association with the intake valve and the exhaust valve of the engine 101 is a cam shaft for setting an intake/exhaust valve timing in synchronism with rotation of the crank shaft. The cam phase actuator 113 serving as the valve timing regulating means is provided in association with the cam shaft and so designed as to change the relative angle (cam phase) between the cam shaft and the crank shaft in the direction for advancing the valve timing (i.e., valve timing advancing direction) or in the direction of retarding the valve timing (i.e., valve timing retarding direction).
An oil control valve (hereinafter also referred to as OCV in abbreviation) 114 is so designed as to regulate the hydraulic pressure supplied to the cam phase actuator 113 to thereby control the cam phase of the cam shaft relative to the crank shaft.
A crank angle sensor 115 disposed in opposition to a sensor plate 116 is so designed as to generate a pulse-like signal upon every passing-by of a projection (not shown) of the sensor plate 116 to thereby detect the angular position (crank angle) of the crank shaft.
The sensor plate 116 for detecting the crank angle is mounted on the crank shaft for corotation therewith and has a tooth or projection (not shown) formed at a predetermined position.
An ECU (Electronic Control Unit) 117 which may be constituted by a microcomputer or microprocessor is so designed as to drive various types of actuators on the basis of detected information derived from the outputs of various sensors which indicate operation state of the engine 101. The ECU is in charge of controlling the cam phase in addition to the control of operation of the engine 101.
Further provided are an oil pump 118 which serves for generating a hydraulic pressure to drive the cam phase actuator 113 and feeding a lubricating oil under pressure to mechanical constituent parts of the engine 101. A hydraulic pressure sensor 119 is provided for detecting the hydraulic pressure of the lubricating oil fed under pressure to the oil control valve 114 from the oil pump 118. Further, an oil temperature sensor 120 is provided for detecting the temperature of the oil fed to the oil control valve 114 from the oil pump 118.
Cooling water 121 is recirculated around the internal combustion engine 101 for cooing it. A water temperature sensor 122 is provided for detecting temperature of the cooling water 121.
All the information detected by the various sensors mentioned above and others is inputted to the ECU 117.
Next, referring to FIGS. 22 to 26 together with FIG. 27, description will be directed to the operation of the conventional valve timing control apparatus of the structure described above.
The control of the valve timing (cam phase) is executed through the oil control valve 114 and the cam phase actuator 113 under the control of the ECU 117.
The ECU 117 is so designed or programmed as to compute or arithmetically determine a desired or target phase angle on the basis of the operation state of the engine 1101. Further, the ECU 117 arithmetically determines a detected phase angle (valve timing) on the basis of the crank angle detected by the crank angle sensor 115 and the cam angle detected by the cam angle sensor 112.
Further, the ECU 117 arithmetically determines an energizing current value (conduction current value) or duty ratio for the oil control valve 114 through feedback control based on an error between the detected phase angle and the target phase angle (i.e., deviation of the former from the latter) so that the detected phase angle coincides with the target phase angle.
The oil control valve 114 selects the oil passage for the cam phase actuator 113 and controls the valve timing by adjusting the hydraulic pressure applied to the cam phase actuator 113.
Now referring to FIGS. 22 to 26, operation of the cam phase actuator (valve timing controller or regulator) 113 will be described in more concrete. In the starting operation of the engine 1101, the oil control valve 114 is so controlled that the hydraulic medium or oil is supplied or fed to the valve timing retarding hydraulic chambers 10 of the cam phase actuator 113.
In this conjunction, it is however noted that in the state where the operation of the engine 1101 is not yet started (i.e., when the engine is stopped), there arises the possibility that the oil within the cam phase actuator 113 and the oil passage extending from the oil pump 118 to the cam phase actuator 113 may be discharged into the oil pan because no hydraulic pressure is applied.
Accordingly, when the engine operation is started, the air (or the oil containing the air) within the oil passage is introduced into the valve timing retarding hydraulic chamber 10 of the cam phase actuator 113. Then, the air (or the air containing oil) introduced into the valve timing retarding hydraulic chambers 10 is discharged exteriorly from the cam phase actuator 113 by way of the purge passage 24, the back pressure chamber 14a and the discharging hole 17.
Once the operation of the engine 1101 has been started, the hydraulic pressure is also introduced into the pin unlocking hydraulic chamber 18a from the valve timing retarding hydraulic pressure distribution passage 23. However, the lock pin 15 is held in the state retained within the retaining hole 18 under the influence of the urging means 16. In this manner, abnormal or foreign noise which would otherwise be generated due to rattling of the second rotor 6 with the lock pin 15 having been released from the retaining hole 18 in the engine starting phase can positively be suppressed.
When a driver of a motor vehicle equipped with the engine system now under consideration depresses an accelerator pedal in succession to the starting of the engine operation with a valve timing advancing command being thus issued from the ECU 117, the oil control valve 114 undergoes such control that the hydraulic pressure is introduced into the valve timing advancing hydraulic chambers 9 of the cam phase actuator 113.
Then, the oil within the valve timing advancing hydraulic chamber 9 is introduced into the pin unlocking hydraulic chamber 18a by way of the valve timing advancing hydraulic pressure distribution passage 22. At that time, the oil control valve 114 is controlled to the position for discharging the oil from the valve timing retarding hydraulic chambers 10. Thus, the oil within the valve timing retarding hydraulic chambers 10 is discharged into the oil pan by way of the oil control valve 114.
Consequently, the lock pin 15 is pushed outwardly from the retaining hole 18 under the hydraulic pressure to be released from the locked state. Now, the second rotor 6 is in the state to operate. More specifically, the second rotor 6 is rotated in the valve timing advancing direction under the hydraulic pressure within the valve timing advancing hydraulic chambers 9. In this way, the valve timing advancing control can be performed for the engine.
However, when the desired or target phase angle changes rapidly from the position at which the lock pin 15 is retained in the retaining hole 18, there will arise such situation that operation of the second rotor 6 starts earlier than releasing or disengaging of the lock pin 15 from the retaining hole 18.
In that case, the lock pin 15 is twisted or tangled or jammed without being withdrawn from the retaining hole 18, making it impossible for the second rotor 6 to operate in the desired direction.
Such being the circumstances, with a view to allowing the rotor 6 to operate smoothly, starting from the state in which the lock pin 15 is retained within the retaining hole 18, the ECU 117 is so designed or programmed as to limit the rate of change of the electric current supplied to the oil control valve 114 for thereby delaying or lowering the operating or moving speed of the rotor 6 so that the ordinary phase feedback control can be executed only after the operation for releasing without fail the lock pin 15 from the locked state has been carried out.
Next, description will be made of exemplary or typical cases in which the valve timing control is inhibited.
Assuming, by way of example only, that the timing for opening the intake valve is advanced, the intake valve will then be opened in the course of the suction stroke. Consequently, the inactive gas is caused to flow backwardly toward the intake side, which will result in that the inactive gas is again charged into the cylinder of the engine 101 in the suction stroke. Consequently, the heat capacity of the air-fuel mixture within the cylinder increases, which incurs lowering of the burning velocity.
When the advancing control of the intake valve open timing is carried out in the cold state of the internal combustion engine, the burning velocity lowers remarkably because it is intrinsically low when the engine 101 is in the state of low temperature, involving thus occurrence of misfire event and fluctuations of the combustion which may unwantedly degrade the drivability of the engine.
For the reasons mentioned above, the ECU 117 is so designed or programmed as to inhibit the control for advancing the intake valve open timing with the aim of suppressing the misfire event and the fluctuation or variation of the combustion when the detected water temperature derived from the output of the water temperature sensor 122 (i.e., the temperature of the cooling water 121 of the engine 101) is lower than a predetermined time.
On the other hand, when the temperature of the cooling water 121 of the engine 101 exceeds the predetermined time, the ECU 117 invalidates or clears the inhibited state of the valve timing advancing control to thereby allow the phase feedback control to be enabled.
In that case, at the time point when the inhibited state of the valve timing advancing control is cleared, the rate of change (also referred to as the change quantity) of the valve timing is limited by limiting the change rate or quantity that of the target phase angle with a view to preventing occurrence of variation or fluctuation of the output torque which may be brought about by abrupt change of the valve timing.
However, in the case where the cam phase actuator is employed which requires unlocking of the lock pin 15 before changing the valve timing such as typified by the one described hereinbefore by reference to FIGS. 22 to 26, the unlocking operation of the lock pin 15 is started from a time point at which the target phase angle has exceeded the predetermined angle with the electric current supplied to the oil control valve 114 being changed slowly.
In that case, the start of change of the valve timing is accompanied with a time lag as compared with the ordinary phase feedback control. Consequently, deviation of the detected phase angle from the target phase angle, i.e., error between the detected phase angle and the target phase angle becomes large at the time point when the unlocked state of the lock pin 15 is detected after the detected phase angle has advanced up to a predetermined angle.
When changeover to the phase feedback control is performed at this time point, the current supplied to the oil control valve 114 becomes large due to a large phase angle error (deviation or difference) between the target phase angle and the detected phase angle, incurring rapid or abrupt change of the valve timing.
If the valve timing changes rapidly in this manner, the output torque of the engine 101 will change, which may result in occurrence of a shock unexpectedly to the driver, to his or her uncomfortableness.
This situation will be described below by reference to FIG. 28 which is a timing chart illustrating how the detected phase angle xcex8a (valve timing) changes as a function of time lapse in the lock pin release control in the conventional apparatus.
In FIG. 28, time is taken along the abscissa with the advance quantity (deg. CA) of the cam phase actuator being taken along the ordinate. As can be seen in FIG. 28, from a time point tps at which the target phase angle xcex8tw which is limited in consideration of the water temperature as ascribed previously (hereinafter also referred to as the water-temperature-limited target phase angle) increases to exceed the predetermined angle (e.g. 5 [deg. CA]), the detected phase angle xcex8a starts to increase, whereupon the control for unlocking the lock pin 15 is started.
On the other hand, the water-temperature-limited target phase angle xcex8tw has already reached a base target phase angle xcex8map at the time point at which the released state of the lock pin 15 is detected. Consequently, if the phase feedback control is performed from this time pint tpe, the detected phase angle xcex8a changes steeply, as can be seen in the figure. As a result of this, the driver experiences unexpectedly a shock due to change of the output torque of the engine.
The conventional valve timing control apparatus for the internal combustion engine suffers a problem that in the case where the cam phase actuator described hereinbefore in conjunction with FIGS. 22 to 26 is employed, changeover to the phase feedback control at the time point tpe when the detected phase angle has advanced up to the predetermined angle (i.e., when the released state of the lock pin 15 is detected), the valve timing changes steeply (see FIG. 28), bringing about change or fluctuation in the output torque of the engine 101 and hence shocks unexpectedly to the driver, to his or her uncomfortableness.
In the light of the state of the art described above, it is an object of the present invention to provide a valve timing control apparatus for an internal combustion engine in which occurrence of a shock unexpectedly to the driver upon changeover to the phase feedback control can be suppressed even in the case where the cam phase actuator which requires operation for releasing the lock pin from the locked state in advance upon changing of the valve timing is employed.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a valve timing control apparatus for an internal combustion engine, which apparatus includes a cam shaft rotatable in synchronism with rotation of a crank shaft of the internal combustion engine for thereby setting valve timing for at least one of an intake valve and an exhaust valve of the engine, a cam phase actuator having a valve timing advancing hydraulic chamber and a valve timing retarding hydraulic chamber to which hydraulic pressure is fed for changing a relative angle of the cam shaft to the crank shaft in a valve timing advancing direction or alternatively in a valve timing retarding direction, a locking mechanism provided in association with the cam phase actuator for locking the relative angle at a predetermined relative angle, an oil pump for generating the hydraulic pressure, a hydraulic pressure regulating means for feeding the hydraulic pressure to the valve timing advancing hydraulic chamber or alternatively to the valve timing retarding hydraulic chamber, and an engine control unit for controlling the hydraulic pressure regulating means.
In the valve timing control apparatus, the locking mechanism is released under the effect of the hydraulic pressure fed to either one of the valve timing advancing hydraulic chamber or the valve timing retarding hydraulic chamber of the cam phase actuator upon changing of the relative angle, while when the relative angle is to be changed from the locked state validated by the locking mechanism, a phase feedback control of the relative angle is performed after having executed a control for releasing the locked state in advance.
Further, the engine control unit mentioned above includes a change quantity limiting means for limiting a change quantity of the valve timing. This means is so designed as to limit the change quantity of the valve timing to a predetermined value upon transition of the locked state releasing control to the phase feedback control.
By virtue of the arrangement described above, there can be realized the valve timing control apparatus for the engine, which apparatus is capable of suppressing positively occurrence of the shock unexpected by the driver upon transition to the phase feedback control, even in the case where the cam phase actuator which requires operation for releasing the lock pin from the locked state in advance upon changing of the valve timing is employed.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.